Separation of polynuclear from mononuclear aromatics



May '25, 1943. A. v. GROSSE ETAL 2,319,813

SEPARATION OF POLYNUCLEAR FROM HONONUCLEAR AROMATICS Filed April; 29, 1940 INVENTOR ABISTID V- GROSSE JULIAN M. MAVITY ATTORNEY Patented May 25, 1943 SEPARATION OF POLYNUCLEAR FROM MONONUCLEAR AROMATICS Aristid V. Grosse, Bronxville,

N. Y., and Julian M.

Mavlty, Chicago, lll., assignors to Universal Oil Products Company, Chicago,

of Delaware 11]., a corporation Application April 29, 1940, Serial No. 332,276

6 Claims.

This invention relates to a process for the separation of polynuciear and mononuclear aromatics.

It is well known that the higher boiling distillates obtained in the distillation or pyrolytic treatment of petroleum hydrocarbons contain large quantities of aromatic compounds. For example, many kerosenes have been found to contain 10-30% of aromatic hydrocarbons. These aromatic hydrocarbons are made up of both mononuclear and polynuclear members. The saturated portion of many kerosenes is highly naphthenic in character and upon thermal or preferably catalytic dehydrogenation, these naphthenic compounds are converted to aromatics. It will thus be seen that the higher boiling petroleum fractions constitute a potential source of an almost unlimited quantity of aromatic hydrocarbons.

In one specific embodiment this invention comprises a process for separating mononuclear and polynuclear aromatic hydrocarbons which comprises subjecting such a mixture to contact with a two-phas solvent system of sulfur dioxide and low boiling paraflins and heating the solution so obtained to evaporate the solvent and to recover the dissolved hydrocarbons.

The purpose of this invention is to provide a method for separating the mononuclear from the polynuclear aromatic hydrocarbons. These aromatic hydrocarbons are of considerable value, particularly in the dye industry. They are not very susceptible to cracking operations and their conversion into motor fuels is accompanied by large losses. By using the process of this invention, a material of relatively little value may be utilized in the preparation of valuable raw materials for other industries, particularly the dye industry.

We have found that it is possible to extract hydrocarbon mixtures consisting essentially of aromatic hydrocarbons with a two-phase solvent consisting, for example, of sulfur dioxide and a low boiling parafiin fraction such as butane or pentane. It is thus possible to concentrate and if desired to separate th polynuclear and mononuclear aromatics. The polynuclear aromatics concentrate in the sulfur dioxide extract leaving the mononuclear aromatics in the raflinate. The process is most effective when some three to five volumes of the paraffin are used per volume of aromatic. If th stock extracted already contains aliphatic hydrocarbons, the quantity of added paraifin may be decreased accordingly.

plus diluent (that is, the paraffin added) should be in the approximate range of 0.25 to 4, depending on the type of oil extracted and the conditions. The process is not limited to continuous type operation, although this method of operation is the most effective. Both the paramn and the sulfur dioxide can be distilled from the raffinate and extract respectively, and reused. The extraction is more selective at low temperatures, for example, 50 to 20 C., but can be successfully used at temperatures up to 30 C.

Diluents other than the low boiling paraflins may be used provided they have low solubility in the second solvent, that is the sulfur dioxide. If th charging stock originally already contains low concentrations of aromatics, the diluent may be dispensed with.

The following examples illustrate the specific operation of the process. It is not intended, however, to limit the invention to the conditions of temperature and concentration disclosed therein, but merely as illustrations of what may be accomplished by the use of the process described.

Example I A mixture containing an equal part by weight of the dinuclear aromatic diphenyl and. the mononuclear aromatic triethyl benzene was diluted with three volumes of normal pentane, cooled to i0 C. and extracted with efiicient stirring on a batch scale with sulfur dioxide. In order to follow the course of the extraction,

- it was carried out in several stages using from The volume of sulfur dioxide per volume of oil 10 to 15% by volume (based on the volume of the diluted mixture) of sulfur dioxide in each stage.

The figure of the accompanying drawing demonstrates how an extract containing about diphenyl was obtained. By the use of sufficient extracting solvent, the reafiinate becomes entirely free of diphenyl and consists of pure triethyl benzene. The figure referred ,to gives the composition of diphenyl in the extract for each of five consecutive extractions. The figure also shows the weight percent of the rafiinate extracted in each of the extractions.

Example II A dehydrogenated Texas kerosene boiling in the range of ZOO-300 C. which was essentially aromatic, was extracted continuously at a temperature of -25 to 30 C. using an oil:bu tane:sulfur dioxide proportion of 2:825. The extract amounted .to 49.5% of the oil charged. Its physical properties and analysis show that it is rich in dinuclear aromatics. Since the original oil contained some saturated material, this was present in the raiilnate with the mononuclear aromatics. The latter were separated from this saturated oil by a second extraction with an oil:pentane:suliur dioxide proportion of 3:322. The character 0! the products is indicated in the accompanying table:

We claim as our invention:

1. A process for separating mononuclear from polynuclear aromatics which comprises subjecting a mixture of said aromatics to solvent extraction with sulfur dioxide in the presence of aliphatic hydrocarbons of low solubility in sulfur dioxide, whereby to concentrate the polynuclear aromatics in the sulfur dioxide extract and and recovering the polynuclear and mononuclear aromatics from said extract and raiiinate respectlvely.

2. The process as defined in claim 1 further characterized in that at least a portion 01' said aliphatic hydrocarbons constitutes a component 01 said mixture.

3. The process as defined in claim 1 further characterized in that at least a portion 01' said aliphatic hydrocarbons is added to said mixture.

4. A separation process which comprises sub- Jecting a hydrocarbon mixture containing mononuclear and polynuclear aromatics to solvent extraction with a two-phase solvent comprising sulfur dioxide and a low boiling parailin, whereby to concentrate the polynuclear aromatics in the sulfur-dioxide extract and leave the mononuclear aromatics in the raillnate. and recovering the polynuclear and mononuclear aromatics from said extract and raillnate respectively.

5. The process as defined in claim 4 further characterized in that said paraflln is butane.

6. The process as defined in claim. 4 further characterized in that said paraflin is pentane.

ARISTID V. GROSSE. JULIAN M. MAYITY. 

